The present invention concerns a process of preparation of amino functionalized diene polymers with 1,4-trans linkage content equal to or greater than 70%. The invention also concerns polymers of such type, a rubber composition and a tire casing containing said polymers. Applicant has described, in French Patent FR-A-2,294,186, a process of polymerization of conjugated dienes or of copolymerization of conjugated dienes, either with other conjugated dienes or with vinylaromatic compounds. The examples of polymers obtained, which appear in that document, present 1,4-trans linkage contents covering a wide range, extending from 24% to 90%.
This process consists essentially of reacting the monomers in the presence of a catalytic composition made up of an organolithium initiator and of a co-catalyst. The latter comprises a barium or strontium compound and an organometallic compound of IIB or IIIA group metals of the periodic classification of elements.
More precisely, said organolithium initiator can be, for example:
an aliphatic organolithium, such as ethyl lithium, n-butyl lithium, isobutyl lithium, sec-butyl lithium, ter-butyl lithium, isopropryl lithium, n-amyl lithium and isoamyl lithium;
an alkene organolithium, such as allyl lithium, propenyl lithium and isobutenyl lithium;
a living polymer, such as polybutadienyl lithium, polyisopropenyl lithium and polystyryl lithium;
a polymethylene dilithium, such as 1,4-dilithiopentane, 1,5-dithiopentane and 1,20-dilithioeicosane;
an aromatic organolithium, such as benzyl lithium, phenyl lithium and 1,1-diphenylmethyl lithium;
a polylithium obtained from an aryl-substituted ethylene compound, the latter being, for example, 1,1-diphenylethylene, trans-stilbene and tetraphenylethylene;
a radical ion, such as lithium naphthalene, lithium anthracene, lithium chrysene and lithium diphenyl;
a derivative substituted by one or more alkyls.
The said barium or strontium compound is, for example, a hydride, or a mono- or polyfunctional organic acid, such as an alcoholate.
As for said organometallic compound of IIB or IIIA group metals, it may be, for example a dialkyl zinc or cadmium, a halogenated or nonhalogenated organoaluminum, an organoborium or a dialkyl aluminum hydride.
One can also cite U.S. Pat. No. 4,996,273, which discloses a process of anionic preparation of polybutadiene having a 1,4-trans linkage content ranging between 82% and 91%, consisting of using an organolithium initiator, a barium, strontium or calcium compound and a trialkylaluminum compound having at least 13 carbon atoms.
It will be noted that neither the FR-A-2,294,186 nor U.S. Pat. No. 4,996,173 mentions obtaining functional polymers.
Also known, from European Patent EP-A-661,298, is a process of preparation of diene polymers which are amino-functionalized and comprise an alkoxysilane group. These polymers are, notably, characterized by a 1,2 linkage content ranging between 14% and 16%, that is, by an overall 1,4-cis and 1,4-trans linkage content ranging between 84 and 86%, which implies a 1,4-trans linkage content very appreciably below 80%, in the order of 60% at most.
This process consists, notably, of using, on the one hand, a lithium amide base catalytic initiator and, on the other, a randomizing agent making it possible to control the 1,2 linkage content in the polymers prepared, and then of reacting the living polymer obtained with an alkoxysilane compound.
Said initiator is, for example lithium hexamethylene imide.
As for said randomizing agent, it can be an ether, an orthodimethoxybenzene, an alkali metal complex and a phosphorous acid ketone or triester, oxygenated derivatives of an alkali or alkaline earth metal, like lithium, sodium, potassium, calcium or barium, or even a tertiary amine.
All of the examples of preparation appearing in EP-A-661,298 refer to processes for obtaining styrene-butadiene copolymers. These processes consist of directly adding the said initiator and the said randomizing agent to the polymerization medium, which consists of styrene and butadiene monomers and of a polymerization solvent.
Concerning the anionic preparation of polymers containing an amino function group, European Patent EP-A-590,491 can also be cited. This document mentions the use of an aminolithium initiator consisting, for example, of hexamethyleneimine, notably, for obtaining styrene and butadiene copolymers presenting a narrow distribution of molecular weights. The copolymers obtained are characterized by vinyl linkage content of at least 34.9%, that is, by 1,4-trans and 1,4-cis linkages equal to not more than 65.1%, which implies an even lower 1,4-trans linkage content.
The present invention provides a process for preparing of amino functionalized diene polymers with 1,4-trans linkage content equal to or greater than 70%. The invention also concerns polymers of such type, a rubber composition and a tire casing containing the polymers.
The process of preparation according to the invention involves polymerizing at least one diene monomer by means of a lithium catalytic system, which consists essentially of at least one hydrocarbon solvent, one compound A of a IIIA group metal, one compound B of an alkaline earth metal and one aminolithium initiator C.
Amino functionalized diene polymers with high 1,4-trans linkage content according to the invention are such that the amino function group, situated at the end of the polymer chain, is a tertiary amnino function group, the rate of functionalization of said polymers being equal to or greater than 50% and the 1,4-trans linkage content being equal to or greater than 70%.
A rubber composition vulcanizable with sulfur according to the invention is such that it contains at least said polymer.
A tire casing according to the invention is such that it contains said composition.
In accordance with this invention, it was sought to employ a new polymerization process which makes it possible to obtain tertiary amino functionalized polymers at chain end and containing a 1,4-trans linkage content which is at least 70%.
For such purpose, according to the invention, the process of preparing amino lunctionalized diene polymers with 1,4-trans linkage content equal to or greater than 70%, which involves polymerizing at least one diene monomer by means of a lithium catalytic system, is characterized in that said catalytic system consists essentially of at least one hydrocarbon solvent, one compound A of a IIIA group metal, one compound B of an alkaline earth metal and one aminolithium initiator C.
As representative examples of the A compounds used, the following organometal compounds can be cited:
halogenated or nonhalogenated organoaluminums such as triethylaluminum, triisobutylaluminum, diethylaluminum chloride, ethylaluminum dichloride, ethylaluminum sesquichloride, and methylaluminum sesquichloride; dialkylaluminum hydrides, such as diethylaluminum hydride, diisobutylaluminum hydride, etc.
A trialkylaluminum compound A is preferably used, the number of carbon atoms of the alkyl group, ranges from 1 to 12, and advantageously trioctylaluminum.
As representative examples of the B compounds used, the following barium or strontium compounds can be cited:
H2Ba and H2Sr hydrides, mono- or polyfunctional organic acids of formulas (Rxe2x80x94COO)2 Ba or Sr, R1xe2x80x94(COO)2 Ba or Sr, in which R and R1 are organic radicals, the first monovalent and the second divalent, the corresponding thioacids, mono- or polyfunctional alcoholates and the corresponding thiolates; mono- or polyfunctional phenates and the corresponding thiophenates; barium or strontium alcohol acid and phenol acid salts and the corresponding thioproducts; barium or strontium xcex2-diketonates such as the reaction products of barium or strontium with acetylacetone, dibenzoylmethane, thenoyltrifluoroacetone, benzoyltrifluoroacetone and benzoylacetone; the organic derivatives of barium or strontium, such as those of 1,1-diphenylethylene, 1,2-acenaphthylene, tetraphenylbutane, a-methylstyrene, or even those such as diphenyl barium or strontium, bis-cyclopentadienyl barium or strontium, trialkysilyl barium or strontium, and triphenylsilyl barium or strontium; mixed organic derivatives such as phenylbarium iodide, methylstrontium iodide, barium or strontium salts of secondary amines; cetyl metals such as barium or strontium benzophenone, barium or strontium cinname and the corresponding alkylated products as well as the sulfur homologues; the radical ions of barium and strontium, such as those of naphthalene, anthracene, chrysene, diphenyl, etc.
A calcium alcoholate can also be used for compound B.
A barium alcoholate is preferably used for said compound B, advantageously, barium ethyldiglycolate or barium nonylphenoxide.
As for the said aminolithium initiator C, it may be preferably a lithium amide or a polymer obtained by anionic means which presents a Cxe2x80x94Li bond and an amino function group.
Said lithium amide preferably corresponds to formula XLi, with X in the X1 or X2 forms corresponding to the following formulas: 
or as described, for example, in the work by T. C. Cheng, Anionic Polymerzation published by the American Chemical Society, Washington, p. 513, 1981, the content of which is incorporated by reference in the present specification. Formula X1 is such that R1 and R2 are each an alkyl group independent of one anotber, the number of carbon atoms of the R1 and R2 set, preferably ranging from 2 to 15. As for formula X2, it comprises a cycloalkyl group, n being a whole number, preferably ranging from 2 to 15.
Preferably, R1 and R2 can each be an ethyl or butyl radical or together form a cycloalkyl radical having 4 to 6 carbon atoms.
Also according to a preferential characteristic of the invention, initiator C is prepared in the absence of a polar agent.
Still more preferably, lithium dibutyl amide or lithium hexamethylene imide is used for C.
According to a first embodiment of the invention, the said catalytic system consists essentially of a co-catalyst, resulting from the reaction product in the said hydrocarbon solvent of said compound A and of said compound B, and of the said initiator C.
According to a first working example of that first embodiment, the process of preparation according to the invention then comprises the following stages:
in a first stage, the said co-catalyst is prepared by reacting the two metal compounds A and B in the said inert hydrocarbon solvent. The mixture obtained is then heated at a temperature ranging between 20xc2x0 C. and 120xc2x0 C. and preferably between 30xc2x0 C. and 50xc2x0 C. and for a duration sufficient to make possible the reaction of both compounds A and B. This duration generally ranges between 1 and 60 minutes and preferably between 20 and 40 minutes;
in a second stage, the said co-catalyst is brought into contact with the polymerization medium containing, for example, one or more monomers dissolved in a polymerization solvent;
in a third stage, the said initiator C is added to the polymerization medium thus obtained, so as to react the mixture obtained in said second stage, and the polymerization reaction is subsequently stopped in order to obtain said polymers, which are then functionalized by a chain-end amino function group. These polymers are recovered as known per se.
According to a second working example of that first embodiment, in which the said initiator C consists essentially of a polymer obtained by anionic means, which presents a Cxe2x80x94Li bond and an amino function group, the process of preparation according to the invention then comprises the following stages:
a first stage is the same as that described for the said first example;
a second stage comprises adding the said polymeric initiator C to the premix obtained in the first stage and formed by compounds A and B, possibly after having added an alkyl lipounds to improve the activity of the catalytic system. Said alkyl lithium compound is preferably butyl lithium;
a third stage comprises adding the catalytic system thus obtained to the said polymerization medium.
The temperature conditions are the same as those of the said first example.
According to a second embodiment of the invention, in which the said initiator C consists essentially of a polymer obtained by anionic means, which presents a Cxe2x80x94Li bond and an amino function group, the said catalytic system consists essentially of a premix of the said compounds A and C in the said hydrocarbon solvent and of the said compound B. More precisely, said premix containing compounds A and C is added to the polymerization medium, and then said compound B is added to all that.
In these two embodiments of the process of preparation according to the invention, one uses a quantity of reagents A and B such that the A/B molar ratio ranges between 0.5 and 5, preferably between 2.5 and 4. One further uses a quantity of both reagents B and C, such that the C/B molar ratio ranges between 0.2 and 4, preferably between 1.5 and 4.
Furthermore, the polymerization solvent is preferably a hydrocarbon solvent, preferably cyclohexane, and the polymerization temperature ranges between 20xc2x0 C. and 150xc2x0 C. and preferably between 60xc2x0 C. and 110xc2x0 C. The alkaline earth metal concentration of the catalytic system ranges between 0.01 molxc2x7lxe2x88x921 and 0.05 molxc2x7lxe2x88x921 and preferably between 0.03 molxc2x7lxe2x88x921 and 0.25 molxc2x7lxe2x88x921.
It will be observed that polymerization according to the invention can be continuous or discontinuous or even be carried out in bulk. The polymers can be block, statistical, sequenced or microsequenced.
An amino-functionalized diene polymer with high 1,4-trans linkage content according to the invention is such that
the amino function group, situated at the end of the polymer chain, is a grafted noncyclic or cyclic tertiary amino function to go that the chain end of the polymer corresponds, according to the circumstance, to the formula: 
xe2x80x83where R1 and R2 are each an alkyl group independent of one another, the number of carbon atoms of the R1 and R2 set preferably ranging from 2 to 15, n being a whole number preferably ranging from 2 to 15,
that the functionalization rate of said polymer is equal to or greater than 50%, and
that the 1,4-trans linkage content is equal to or greater than 70%.
Such a polymer according to the invention, comprising an amino function group and presenting a high 1,4-trans linkage content, is notably intended to be incorporated in a rubber composition vulcanizable with sulfur, containing a reinforcing filler, which can be based on a reinforcing white filler or carbon black filler.
Reinforcing white filler is understood to mean a white filler capable of alone reinforcing, with no means other than a filler/intermediate elastomer matrix bonding agent, to provide a rubber composition intended for the manufacture of tires, capable in other words of replacing in its reinforcing function a conventional carbon black filler of tire grade.
Such a reinforcing white filler can, for example, be made of silica.
As silica capable of being used in a composition according to the invention, all the precipitated or pyrogenated silicas known to the expert are suitable, with a BET surface value equal to or less than 450 m2/g and a CTAB specific surface value equal to or less than 450 m2/g, with highly dispersible precipitated silicas being preferred.
Highly dispersible silica is understood to mean any silica having a capacity for disagglomeration and dispersion in a very large polymeric matrix observable by electron or optical microscopy on fine sections. The dispersibility of silica is also appreciated by means of an ultrasonic disagglomeration capacity test followed by a measurement, by granulometric diffraction, of the size of the silica particles, in order to determine the median diameter (D50) of the particles and the disagglomeration factor (Fd) after disagglomeration, as described in patent EP-A-520,860, the content of which is incorporated herein, or as also described in the article that appeared in Rubber World (June 1994), pp. 20-24, Dispersibility Measurements of prc. silicas, also incorporated herein by reference.
As nonlimiting examples of such preferred highly dispersible silicas, one can mention those having a CTAB surface of value equal to or less than 450 ml/g and, in particular, those described in European Patents EP-A-157,703 and EP-A-520,862, or the Perkasil KS 430 silica of the AKZO company, the Zeosil 1165 MP and 85 MP silicas of the Rhodia company, the HI-Sil 2000 silica of the PPG company and the Zeopol 8741 or 8745 silicas of the Huber company.
However, the silicas preferably suitable are those having:
a CTAB specific surface value ranging between 30 and 250 m2/g and preferably between 60 and 200 m2/g,
a BET specific surface value ranging between 30 and 300 m2/g and preferably between 70 and 240 m2/g,
a DOP oil absorption value less than 300 ml/100 g and preferably between 200 and 295 ml/100 g,
a median diameter (D50), after ultrasonic disagglomeration, equal to or less than 3 microns and preferably less than 2.8 microns, for example, less than 2.5 microns,
an ultrasonic disagglomeration factor (Fd) greater than 10 ml, preferably greater than 11 ml and, more preferably, equal to or greater than 21 ml,
a BET specific surface/CTAB specific surface ratio, the value of which ranges between 1.0 and 1.2.
The physical state of the silica does not matter, whether it is in the form of powder, microbeads, granules or balls.
Of course, silica is also understood to mean mixtures of different silicas. Silica can be used alone or in the presence of other white fillers. The CTAB specific surface value is determined according to the method of the NFT 45007 standard of November 1987. The BET specific surface value is determined according to the method of Brunauer, Emmet and Teller, J. Amer. Chem. Soc. 80:309 (1938), corresponding to the NFT 45007 standard of November 1987.
One can also use as reinforcing white filler, on a nonlimiting basis:
aluminas (of formula Al2O3), such as the high-dispersibility aluminas described in European Patent EP-A-810,258, or
aluminum hydroxides, such as those described in international patent WO-A-99/28376.
According to another working example of a composition of the invention, said reinforcing filler can be carbon black.
All blacks commercially available or conventionally used in tires and, in particular, in treads are suitable as carbon blacks. As nonlimiting examples, the N234, N339, N326 and N375 blacks can be cited.
Carbon black/silica mixtures or the blacks partially or totally coated with silica are also suitable for the invention.
Carbon blacks modified by silica are likewise suitable as reinforcing filler, such as, on a nonlimiting basis, the fillers marketed by the Cabot company under the xe2x80x9cCRX 2000xe2x80x9d name and described in international patent WO-A-96/37547.
The reinforcing filler proportion can vary from 30 to 100 parts by weight per 100 parts polymer according to the invention.
It will be observed that the polymers obtained according to the invention can advantageously be functionalized by different electrophilic coupling agents in order to produce a function interactive with the aforesaid filler. One can, notably, mention, for these coupling agents, tin derivatives such as those cited in Japanese Patent JP-A-1,135,847, and amino derivatives such as those cited in U.S. Pat. Nos. 5,248,736, 5,281,671, 4,647,625 and 5,001,196.
The rubber composition according to the invention can further embrace, in standard fashion, when the reinforcing filler is a reinforcing white filler, a white filler/elastomer matrix bonding agent, which has the function of ensuring a sufficient bond, of a chemical and/or physical nature, between said white filler and the matrix, while facilitating the dispersion of that white filler in said matrix.
Filler/polymer bonding agents can be used, for example, comprising the alkoxysilanes mentioned in European Patent EP-A-692,493.
In addition, a rubber composition according to the invention can further contain the other constituents and additives customarily used in rubber compounds, such as plasticizers, pigments, antioxidants, condensation catalysts, sulfur, vulcanization accelerators, dilute oils, etc.
The resulting composition according to the invention advantageously presents, in vulcanized state, improved hysteretic properties.
Such a rubber composition according to the invention is intended to be incorporated in a tire casing, with a reduction of the tire rolling resistance resulting from said improved hysteretic properties.
The aforesaid characteristics of this invention, as well as others, will be better understood by reading the following description of several working examples of the invention, given by way of nonlimitative illustration.
The term xe2x80x9cpolymerxe2x80x9d below covers both homopolymers and copolymers, the term xe2x80x9ccopolymerxe2x80x9d covering the polymers each obtained from two or more than two monomers, such as terpolymers.
Diene polymer is understood to mean any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms, and any copolymer obtained by copolymerization of one or more dienes conjugated with each other or with one or more vinylaromatic compounds having from 8 to 20 carbon atoms. One can mention as conjugated diene, notably, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(alkyl in C1 to C5)-1,3-butadienes such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene.
Styrene, ortho-, meta- and paramethylstyrene, the xe2x80x9cvinyltoluenexe2x80x9d commercial mixture, paratertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinylmesithylene, divinylbenzene and vinylnaphthalene are, notably, suitable as vinylaromatic compounds.
Two examples (1 and 2) are presented below of known processes for the preparation of polymers with high 1,4-trans linkage content, as well as eight preferential examples according to the invention for the preparation of tertiary amino functionalized polymers having a 1,4-trans linkage content greater than 60% (Examples 3 to 8).
The inherent viscosities mentioned below were established at 25xc2x0 C. in 0.1 g/dl toluene solution.